Apparatus for manufacturing holographic optical element, and apparatus for reconstructing holograms

ABSTRACT

An apparatus for manufacturing a hologram includes a holographic optical element on which a first interference pattern of a first signal beam and a first reference beam is recorded and a second interference pattern of a second signal beam modulated by a Fourier lens and a second reference beam is recorded. Also, an apparatus for reconstructing a hologram by using the holographic optical element is provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2016-0148185, filed on Nov. 8, 2016, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND

1. Field

One or more embodiments relate to an apparatus for manufacturing aholographic optical element, and an apparatus for reconstructing aholographic image by using the holographic optical element.

2. Description of the Related Art

Recently, there has been a great demand for a three-dimensional imagedisplay device capable of realistically and effectively realizing imagesin various fields such as movies, games, advertisements, medicalimaging, education, military, etc. Accordingly, various techniques fordisplaying a three-dimensional image have been proposed, and variousthree-dimensional image display devices have already beencommercialized.

Three-dimensional image display devices include, for example, a glassestype and a non-glasses type. Furthermore, the glasses type includes apolarized glasses type and a shutter glasses type. The non-glasses typeincludes a stereoscopy type which includes a lenticular type using aplurality of cylindrical lens arrays and a parallax barrier type havinga plurality of barriers and openings.

A hologram method and an integral imaging method have been proposed as athree-dimensional image display method in which depth perceptionrecognized by the brain matches the focal point of the eyes and whichcan provide full parallax.

A hologram, which is a medium on which a light wave is recorded, storesintensity and phase information of the light wave. While ordinaryphotographs only record intensity information, holograms store bothintensity and phase, thus enabling three-dimensional reconstruction ofvisual information. For recording a hologram, two beams including asignal beam and a reference beam, both having coherence, are required.The signal beam is a beam that can be modulated from an object to berecorded. The intensity or phase information of an interference patternbetween the signal beam and the reference beam is recorded in a hologramrecording medium, and thus the intensity or phase information of amodulated signal beam can be recorded. When a beam having the sameoptical characteristics as the reference beam used for recording isincident on the recorded hologram, the signal beam stored in thehologram can be reproduced.

SUMMARY

One or more embodiments include a apparatus for manufacturing aholographic optical element, and apparatus for reconstructing aholographic image by using the holographic optical element

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to one or more embodiments, an apparatus for manufacturing aholographic optical element having different optical characteristicsincludes: a light emitting portion configured to sequentially emit afirst laser beam and a second laser beam; a beam splitter configured tosplit the first laser beam into a first signal beam and a firstreference beam, and split the second laser beam into a second signalbeam and a second reference beam; a hologram recording medium; a firstoptical system configured to emit the first signal beam to one surfaceof the hologram recording medium and the first reference beam to anothersurface of the hologram recording medium, and to record a firstinterference pattern of the first signal beam and the first referencebeam on the hologram recording medium; and a second optical systemcomprising a Fourier lens and configured to emit a second signal beammodulated by the Fourier lens to one surface of the hologram recordingmedium and a second reference beam to another surface of the hologramrecording medium, and to record a second interference pattern of themodulated second signal beam and the second reference beam on thehologram recording medium.

Energy of the modulated second signal beam and the second reference beamemitted to the hologram recording medium during recording of the secondinterference pattern may be set to be greater than energy of the firstsignal beam and the first reference beam emitted to the hologramrecording medium during recording of the first interference pattern.

The light emitting portion may emit the second laser beam longer than anemission time of the first laser beam.

The hologram recording medium, on which the first interference patternand the second interference pattern are recorded, may have opticalcharacteristics of a mirror corresponding to the first interferencepattern and optical characteristics of a Fourier lens corresponding tothe second interference pattern.

According to one or more embodiments, an apparatus for reconstructing ahologram includes: a holographic optical element on which a firstinterference pattern of a first signal beam and a first reference beamis recorded and a second interference pattern of a second signal beammodulated by a Fourier lens and a second reference beam is recorded; aspatial light modulator; and a light source configured to emit a firststandard beam to the holographic optical element, corresponding to thefirst reference beam, wherein the holographic optical element, inresponse to the first standard beam, reconstructs a first reconstructionbeam corresponding to the first signal beam, and emits the firstreconstruction beam to the spatial light modulator, the spatial lightmodulator generates a second standard beam by modulating the firstreconstruction beam according to hologram information, and emits thesecond standard beam to the holographic optical element, correspondingto the second reference beam, and the holographic optical elementreconstructs a holographic image by focusing the second standard beam ina space.

Energy of the modulated second signal beam and the second reference beamemitted during recording of the second interference pattern may be setto be greater than energy of the first signal beam and the firstreference beam emitted during recording of the first interferencepattern.

The first standard beam and the second standard beam may satisfy aBragg's matching condition with the first reference beam and the secondreference beam, respectively.

The hologram information may be information about a computer-generatedhologram.

The second standard beam may indicate a Fourier-transformedcomputer-generated hologram, and the holographic optical element mayperform an inverse Fourier transform on the Fourier-transformedcomputer-generated hologram to generate the holographic image.

The spatial light modulator may generate the second standard beam bymodulating the first reconstruction beam according to holograminformation considering an angular difference between the spatial lightmodulator and the holographic optical element.

The apparatus may further include: a plurality of polarized panelsarranged in front of and in the rear of the spatial light modulator in aperpendicular direction with each other; and a half bandpass filter.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of an apparatus for manufacturing aholographic optical element according to an embodiment;

FIG. 2 schematically illustrates that the apparatus of FIG. 1 records afirst record pattern of a first signal beam and a first reference beamon a hologram recording medium through a first optical system;

FIG. 3 schematically illustrates that the apparatus of FIG. 1 records asecond record pattern of a second signal beam modulated by a Fourierlens and a second reference beam on a hologram recording medium througha second optical system;

FIG. 4 illustrates in detail a process of recording an interferencepattern of a second reference beam and a second signal beam modulated bya Fourier lens on a hologram recording medium, according to anembodiment;

FIG. 5 schematically illustrates an apparatus for reconstructing ahologram, according to an embodiment;

FIGS. 6A and 6B illustrate a detailed example in which the holographicoptical element reconstructs a first reconstruction beam in response tothe first standard beam;

FIGS. 7A and 7B illustrate a detailed example in which the holographicoptical element reconstructs a second reconstruction beam in response tothe second standard beam;

FIG. 8 illustrates an example in which a spatial light modulatorgenerates a second standard beam according to hologram information, andan example in which the holographic optical element generates a secondreconstruction beam by performing a Fourier transform on the secondstandard beam;

FIG. 9 illustrates a phenomenon that the size of a pixel is distortedaccording to the oblique incidence of the second standard beam;

FIG. 10 schematically illustrates an apparatus for reconstructing ahologram, according to another embodiment; and

FIGS. 11A, 11B, and 11C illustrate an example in which the apparatus forreconstructing a hologram displays a holographic image.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentembodiments may have different forms and should not be construed asbeing limited to the descriptions set forth herein. Accordingly, theembodiments are merely described below, by referring to the figures, toexplain aspects of the present description.

The terms used in the present inventive concept have been selected fromcurrently widely used general terms in consideration of the functions inthe present inventive concept. However, the terms may vary according tothe intention of one of ordinary skill in the art, case precedents, andthe advent of new technologies. Also, for special cases, meanings of theterms selected by the applicant are described in detail in thedescription section. Accordingly, the terms used in the presentinventive concept are defined based on their meanings in relation to thecontents discussed throughout the specification, not by their simplemeanings.

When a part may “include” a certain constituent element, unlessspecified otherwise, it may not be construed to exclude anotherconstituent element but may be construed to further include otherconstituent elements.

The present inventive concept will now be described more fully withreference to the accompanying drawings, in which embodiments of theinventive concept are shown. Throughout the drawings, like referencenumerals denote like elements. In the following description, whendetailed descriptions about related well-known functions or structuresare determined to make the gist of the present inventive conceptunclear, the detailed descriptions will be omitted herein.

FIG. 1 is a block diagram of an apparatus 100 for manufacturing aholographic optical element according to an embodiment.

Referring to FIG. 1, the apparatus 100 for manufacturing a holographicoptical element may include a light emitting portion 110, a beamsplitter 120, a hologram recording medium 150, a first optical system130, and a second optical system 140. In FIG. 1, only constituentelements related to the apparatus 100 according to the presentembodiment are illustrated. Accordingly, a person having ordinary skillin the art may understand that, in addition to the constituent elementsillustrated in FIG. 1, the apparatus 100 can further include othercommon constituent elements.

The light emitting portion 110 according to the present embodiment maysequentially emit a first laser beam and a second laser beam. In otherwords, the light emitting portion 110 may emit the first laser beam fora certain time and then the second laser beam for a certain time.

The beam splitter 120 according to the present embodiment may split afirst laser beam emitted from the light emitting portion 110 into afirst signal beam and a first reference beam. Furthermore, the beamsplitter 120 according to the present embodiment may split the secondlaser beam emitted from the light emitting portion 110 into a secondsignal beam and a second reference beam. According to the presentembodiment, the beam splitter 120 may be a half mirror, by which about50% of an incident beam is transmitted to be used as a reference beamand about 50% of the incident beam is reflected to be used as a signalbeam.

The first optical system 130 a allows the first signal beam to beincident on one surface of the hologram recording medium 150, and thefirst reference beam to be incident on the other surface of the hologramrecording medium, and thus a first interference pattern of the firstsignal beam and the first reference beam maybe recorded on the hologramrecording medium 150. A detailed example thereof is described below withreference to FIG. 2.

The second optical system 140 may include a Fourier lens, which allowsthe second signal beam modulated by the Fourier lens to be incident onone surface of the hologram recording medium 150 and the secondreference beam to be incident on the other surface of the hologramrecording medium 150. Thus, a second interference pattern of themodulated second signal beam and the second reference beam may berecorded on the hologram recording medium 150. A detailed embodimentthereof is described below with reference to FIG. 3.

The hologram recording medium 150 may include, for example, silverhalide, photorefractive polymer, photopolymer, etc.

Accordingly, the apparatus 100 may manufacture a holographic opticalelement by recording the first interference pattern and the secondinterference pattern on the hologram recording medium 150. Theholographic optical element manufactured by the apparatus 100 may havedifferent optical characteristics, in particular, the opticalcharacteristics according to the first interference pattern andsimultaneously the optical characteristics according to the secondinterference pattern. For example, the holographic optical element mayhave the optical characteristics of a “mirror” according to the firstinterference pattern, and simultaneously have the opticalcharacteristics of a “Fourier lens” according to the second interferencepattern.

FIG. 2 schematically illustrates that the apparatus 100 of FIG. 1records the first record pattern of the first signal beam and the firstreference beam on the hologram recording medium 150 through the firstoptical system 130.

According to the present embodiment, the first optical system 130 mayinclude a first mirror 132, a second mirror 134, and a third mirror 136.

The light emitting portion 110 may emit the first laser beam, and thebeam splitter 120 may split the first laser beam into the firstreference beam and the first signal beam. However, although FIG. 2illustrates that a light passing through the beam splitter 120 is thefirst reference beam and a light reflected from the beam splitter 120 isthe first signal beam, this is merely exemplary. For example, in anotherembodiment, the optical arrangement of the apparatus 10 may be changedsuch that the light passing through the beam splitter 120 is the firstsignal beam, and the light reflected from the beam splitter 120 is thefirst reference beam.

Next, the first mirror 132 of the first optical system 130 may reflectthe first signal beam split from the beam splitter 120 to be incident onone surface of the hologram recording medium 150. Furthermore, thesecond mirror 134 and the third mirror 136 of the first optical system130 may reflect the first reference beam split from the beam splitter120 to be incident on the other surface of the hologram recording medium150.

The first optical system 130 may further include an aperture (not shown)to adjust an area of the first signal beam and the first reference beamemitted to the hologram recording medium 150.

Accordingly, the first interference pattern may be formed as the firstreference beam and the first signal beam meet each other. The firstinterference pattern formed as above may be recorded on the hologramrecording medium 150.

Furthermore, the first mirror 132, the second mirror 134, and the thirdmirror 136 of the first optical system 130 may adjust angles at whichthe first signal beam and the first reference beam are emitted to thehologram recording medium 150.

FIG. 3 schematically illustrates that the apparatus 100 of FIG. 1records the second record pattern of the second signal beam modulated bya Fourier lens 144 and the second reference beam on the hologramrecording medium 150 through the second optical system 140.

According to the present embodiment, the second optical system 140 mayinclude a first mirror 142, the Fourier lens 144, and a second mirror146. According to the present embodiment, the first mirror 142 may be ina form of moving the first mirror 132 of FIG. 2, and the second mirror146 may be in a form of rotating the second mirror 134 of FIG. 2. Forexample, the second optical system 140 may further include a stage (notshown) that is motorized to be moved, and the first mirror 132 and thesecond mirror 134 of FIG. 2 may be moved or rotated by means of thestage.

The light emitting portion 110 may emit the second laser beam, and thebeam splitter 120 may split the second laser beam into the secondreference beam and the second signal beam. However, although FIG. 3illustrates that the light passing through the beam splitter 120 is thesecond reference beam and the light reflected from the beam splitter 120is the second signal beam, this is merely exemplary. For example, inanother embodiment, the optical arrangement of the apparatus 100 may bechanged such that the light passing through the beam splitter 120 is thesecond signal beam and the light reflected from the beam splitter 120 isthe second reference beam.

Next, the first mirror 142 of the second optical system 140 may reflectthe second signal beam split by the beam splitter 120 to beperpendicularly incident on the Fourier lens 144. Accordingly, thesecond signal beam reflected from the first mirror 142 may be modulatedwhile passing through the Fourier lens 144, and the modulated secondsignal beam may be incident on one surface of the hologram recordingmedium 150. Furthermore, the second mirror 146 of the second opticalsystem 140 may reflect the second reference beam split by the beamsplitter 120 to be incident on the other surface of the hologramrecording medium 150 at a preset angle. Furthermore, the apparatus 100may adjust the preset angle by beams of the second mirror 146.

The Fourier lens 144 may have a characteristic to perform a Fouriertransform or an inverse Fourier transform on an incident beam withrespect to a spatial frequency according to an embodiment.

The second optical system 140 may further include an aperture (notshown) to adjust an area of the second signal beam and the secondreference beam emitted to the hologram recording medium 150.

Accordingly, the second interference pattern may be formed as the secondreference beam and the second signal beam meet each other through theFourier lens 144. The second interference pattern formed as above may berecorded on the hologram recording medium 150.

FIG. 4 illustrates in detail a process of recording the interferencepattern of the second reference beam and the second signal beammodulated by the Fourier lens 144 on the hologram recording medium 150,according to an embodiment.

As illustrated in FIG. 4, the second reference beam, as a plane-wave, isemitted to the hologram recording medium 150. Furthermore, the secondsignal beam of a plane-wave passes through the Fourier lens 144 to bemodulated into a spherical-wave having the optical characteristics ofthe Fourier lens 144, and is emitted to the hologram recording medium150. The second reference beam and the modulated second signal beam meeteach other forming an interference pattern, and the formed interferencepattern is recorded on the hologram recording medium 150. The hologramrecording medium 150 where the interference pattern is recorded maydenote a holographic optical element.

The apparatus 100 may record the first interference pattern of the firstreference beam and the first signal beam on the hologram recordingmedium 150, through the embodiment of FIG. 2, and then the secondinterference pattern of the second reference beam and the second signalbeam modulated by the Fourier lens 144 on the hologram recording medium150, through the embodiment of FIG. 3. According to an embodiment, theapparatus 100 may set the energy of the modulated second signal beam andthe second reference beam emitted to the hologram recording medium 150for the recording of the second interference pattern, to be greater thanthe energy of the first signal beam and the first reference beam emittedto the hologram recording medium 150 for the recording of the firstinterference pattern. For example, when the laser beam emitted from thelight emitting portion 110 has the same energy quantity per hour, thelight emitting portion 110 emits the second laser beam longer than anemission time of the first laser beam, and thus the energy of themodulated second signal beam and the second reference beam for therecording of the second interference pattern may be set to be greaterthan the energy of the first signal beam and the first reference beamfor the recording of the first interference pattern. According to anembodiment, to equate diffraction efficiency of the holographic opticalelement with respect to the optical characteristics of the firstinterference pattern and diffraction efficiency of the holographicoptical element with respect to the optical characteristics of thesecond interference pattern, the apparatus 100 may set the energy of themodulated second signal beam and the second reference beam for therecording of the second interference pattern to be greater than theenergy of the first signal beam and the first reference beam for therecording of the first interference pattern.

Furthermore, although FIGS. 2 and 3 illustrate that the apparatus 100uses a reflection hologram recording method in which the signal beam andthe reference beam are respectively incident on both surfaces of thehologram recording medium 150, according to another embodiment, theapparatus 100 may adopt a transmission hologram recording method inwhich the signal beam and the reference beam are incident on one surfaceof the hologram recording medium 150.

FIG. 5 schematically illustrates an apparatus 500 for reconstructing ahologram, according to an embodiment.

The apparatus 500 for reconstructing a hologram according to the presentembodiment may include a holographic optical element 510, a light source520, and a spatial light modulator 530. In FIG. 5, only constituentelements related to the apparatus 500 for reconstructing a hologramaccording to the present embodiment are illustrated. Accordingly, aperson having ordinary skill in the art may understand that, in additionto the constituent elements illustrated in FIG. 5, the apparatus 500 canfurther include other common constituent elements.

The holographic optical element 510 may be a hologram recording mediumon which the first interference pattern of the first signal beam and thefirst reference beam is recorded and the second interference pattern ofthe second signal beam modulated by the Fourier lens 144 and the secondreference beam are recorded. According to an embodiment, the holographicoptical element 510 may be a holographic optical element manufactured bythe apparatus 100 of FIGS. 1 to 3.

The light source 520 may emit a first standard beam to the holographicoptical element 510, according to an embodiment. In particular, thelight source 520 may emit the first standard beam to the holographicoptical element 510 corresponding to the first reference beam. Indetail, since the first reference beam used in the process of recordingthe first interference pattern on the holographic optical element 510 isa collimated light, to satisfy the Bragg's matching condition, the lightsource 520 may project a collimated light toward the holographic opticalelement 510. Bragg's matching denotes that a hologram recorded by areference beam and a signal beam having a specific angle therebetween isreconstructed strongly depending on the angel between the reference beamduring recording and the beam during reconstruction. In other words, forexample, since the reference beam is incident at an angel θ in therecording process of the holographic optical element 510, the lightsource 520 may project a collimated light toward the holographic opticalelement 510 at an angle θ.

The holographic optical element 510, in response to the first standardbeam emitted from the light source 520, may reconstruct the firstreconstruction beam corresponding to the first signal beam, and may emitthe first reconstruction beam toward the spatial light modulator 530. Indetail, the holographic optical element 510 may receive the firststandard beam satisfying the Bragg's matching condition with the firstreference beam used in the recording process of the first interferencepattern. Accordingly, the holographic optical element 510 mayreconstruct the first signal beam used in the recording process of thefirst interference pattern as the first reconstruction beam.

FIGS. 6A and 6B illustrate a detailed example in which the holographicoptical element reconstructs a first reconstruction beam in response tothe first standard beam.

Referring to FIG. 6A, during the manufacture of the holographic opticalelement 510, the first interference pattern by the first reference beamemitted at the angle θ with the first signal beam may be recorded on thehologram recording medium 150.

In FIG. 6B, when the first standard beam emitted from the light source520 at the angle θ, the holographic optical element 510 may emit thefirst reconstruction beam toward the spatial light modulator 530 byreconstructing the first reconstruction beam corresponding to the firstsignal beam.

Referring back to FIG. 5, the spatial light modulator 530 may modulatethe first reconstruction beam emitted from the holographic opticalelement 510 according to hologram information, thereby generating asecond standard beam. In other words, the spatial light modulator 530may generate the first reconstruction beam modulated according to thehologram information, as the second standard beam. In detail, thespatial light modulator 530 may transform the first reconstruction beaminto the second standard beam that is an image formed of bright dots anddark dots, according to an electric signal including digitalinformation. According to an embodiment, the hologram information may beinformation about a computer-generated hologram, and the spatial lightmodulator 530 may modulate the first reconstruction beam and thusgenerate the second standard beam that indicates a Fourier-transformedcomputer-generated hologram. According to an embodiment, the spatiallight modulator 530 may be a reflective spatial light modulator, and mayemit the generated second standard beam toward the holographic opticalelement 510. According to an embodiment, the spatial light modulator 530may be an amplitude-type spatial light modulator.

Furthermore, according to an embodiment, as the second standard beamfrom the spatial light modulator 530 has oblique incidence with theholographic optical element 510, the second standard beam of the spatiallight modulator 530 having a pixel size may appear to have a distortedpixel size on the holographic optical element 510. Accordingly, since aratio of a horizontal length and a vertical length of the holographicimage reconstructed according to the distortion phenomenon may vary, tocorrect the distortion phenomenon in advance, the spatial lightmodulator 530 may generate the second standard beam according tohologram information considering the angular difference between theholographic optical element 510 and the spatial light modulator 530. Adetailed embodiment is presented below with reference to FIG. 9.

Furthermore, according to an embodiment, the apparatus 500 forreconstructing a hologram may further include a separate processor (notshown). The apparatus 500 for reconstructing a hologram may generatehologram information by using the processor, in particular, holograminformation about Fourier-transformed computer-generated hologram.

The holographic optical element 510 may reconstruct the secondreconstruction beam indicating a holographic image, in response to thesecond standard beam emitted from the spatial light modulator 530. Indetail, the holographic optical element 510 may receive the secondreference beam used in the process of recording the second interferencepattern and the second standard beam satisfying the Bragg's matchingcondition, and may reconstruct the second reconstruction beam indicatinga holographic image by focusing in a space the second standard beamaccording to the optical characteristics of the Fourier lens used whenthe recorded second interference pattern is recorded. In other words,the second standard beam indicates a Fourier-transformedcomputer-generated hologram. The holographic optical element 510 mayperform an inverse Fourier transform on the second standard beam,according to the optical characteristics of the Fourier lens, and mayreconstruct the second reconstruction beam indicating a holographicimage.

FIGS. 7A and 7B illustrate a detailed example in which the holographicoptical element reconstructs a second reconstruction beam in response tothe second standard beam;

Referring to FIG. 7A, during the manufacture of the holographic opticalelement 510, the second interference pattern by the second referencebeam emitted at the angle θ with the second signal beam modulated by theFourier lens 144 may be recorded on the hologram recording medium 150.Accordingly, the holographic optical element 510 may have the opticalcharacteristics of the Fourier lens 144 with respect to the lightsatisfying the Bragg's matching condition.

In FIG. 7B, when the second standard beam emitted from the spatial lightmodulator 530 at the angle θ, the holographic optical element 510 mayfocus in a space the second standard beam according to the opticalcharacteristics of the Fourier lens 144 and may reconstruct the secondreconstruction beam indicating a three-dimensional hologram image.

FIG. 8 illustrates an example in which the spatial light modulator 530generates the second standard beam according to the holograminformation, and an example in which the holographic optical element 510generates the second reconstruction beam by performing a Fouriertransform on the second standard beam.

Referring to FIG. 8, when the wave function of an object to bereconstructed as a hologram is “g(x,y)”, the spatial light modulator 530may modulate the first reconstruction beam according to the holograminformation, and may generate the second standard beam indicating theFourier-transformed computer-generated hologram that is “H(ξ,η)”. Asillustrated in FIG. 8, not only a real term but also an imaginary termmay be generated by a Fourier transform, and it is impossible togenerate the imaginary term as the second standard beam, it may be seenthat, instead of directly using “G(f_(x),f_(y))”, “H(ξ,η)” that is a sumwith a conjugate term “G*(f_(x),f_(y))” is used.

Next, the holographic optical element 510 may perform an inverse Fouriertransform on the second standard beam indicating “H(ξ,η)” according tothe optical characteristics of the Fourier lens 144, and thus the secondreconstruction beam that is a holographic image with respect to “g(x,y)”may be reconstructed. As illustrated in FIG. 8, “g*(x,y)” and “δ(x,y)”may be generated as a result of the inverse Fourier transform of theholographic optical element 510. The apparatus 500 for reconstructing ahologram may further include a filtering portion (not shown), and thus“g*(x,y)” and “δ(x,y)” may be removed through filtering.

FIG. 9 illustrates a phenomenon that the size of a pixel is distortedaccording to the oblique incidence of the second standard beam.

Referring to FIG. 9, when the second standard beam emitted from thespatial light modulator 530 is incident on the holographic opticalelement 510 at the angle θ, the second reference beam of the spatiallight modulator 530 having a pixel size px may expand to a size ofpx/cos(θ) on the holographic optical element 510. Furthermore, since thesize of a holographic image may be reduced as the pixel size increases,the size of an image may be distorted. Accordingly, to correct thedistortion phenomenon in advance, the apparatus 500 for reconstructing ahologram may generate the second standard beam according to the holograminformation considering the angle θ. For example, since the size of aholographic image may be reduced in a horizontal direction, theapparatus 500 for reconstructing a hologram may correct the distortionin advance in the process of generating a computer-generated hologram.

Referring back to FIG. 5, an observer 540 may see a holographic imagereconstructed by the holographic optical element 510. Furthermore, theholographic optical element 510 having the characteristics of passing alight that does not satisfy the Bragg's matching condition among thelights incident on the holographic optical element 510, may have asee-through characteristic. Accordingly, the holographic optical element510 may satisfy a see-through condition with no reduction of actualbrightness that is an essential requirement in optical see-throughaugmented reality.

Accordingly, the apparatus 500 for reconstructing a hologram accordingto the present embodiment may be used for portable devices, head-updisplay devices, three-dimensional display devices, image screens, etc.,which may implement the optical see-through augmented reality.

FIG. 10 schematically illustrates an apparatus for reconstructing ahologram, according to another embodiment.

Referring to FIG. 10, the apparatus 500 for reconstructing a hologramaccording to the present embodiment may further include a firstpolarized panel 1010, a second polarized panel 1020, and a half bandpassfilter 1030.

The first polarized panel 1010 and the second polarized panel 1020 maybe arranged in front of and in the rear of the spatial light modulator530 along an optical path in a perpendicular direction with each other,and thus the spatial light modulator 530 may be operated in an amplitudemode. In other words, the first polarized panel 1010 may be arranged ona path of the first reference beam, and the second polarized panel 1020may be arranged on a path of the second reconstruction beam.

The half bandpass filter 1030 may be arranged on a Fourier plane, andmay perform filtering on an undesired image and signal of theholographic image. For example, in FIG. 8, the half bandpass filter 1030may filter and remove the conjugate term “g*(x,y)” and a direct current(DC) term “δ(x,y)”.

FIGS. 11A, 11B, and 11C illustrate an example in which the apparatus forreconstructing a hologram displays a holographic image.

FIGS. 11A, 11B, and 11C are holographic images photographed by replacingthe position of the observer 540 with a camera.

FIG. 11A shows an image photographed when the focus of a camera islocated on a Fourier plane. FIG. 11B shows an image photographed whenthe focus of a camera is located on the holographic optical element.FIG. 11C shows an image photographed when the focus of a camera islocated at a background object in the rear of the holographic opticalelement.

Accordingly, as illustrated in FIG. 11, the apparatus 500 forreconstructing a hologram according to the present embodiment mayimplement the optical see-through augmented reality, and thus, in viewof an observer, not only a three-dimensional holographic image, but alsothe background object in the rear of the holographic optical element,may be observed without distortion.

As described above, the holographic optical element according to thepresent disclosure may implement the optical see-through augmentedreality and have the optical characteristics of the Fourier lens. Theapparatus for reconstructing a hologram may reconstruct athree-dimensional holographic image by means of the holographic opticalelement. Also, in view of an observer, not only a three-dimensionalholographic image, but also a background object located in the rear ofthe holographic optical element may be observed without distortion.

Furthermore, since the first interference pattern and the secondinterference pattern are recorded together in the holographic opticalelement according to the present disclosure, the holographic opticalelement may have different optical characteristics corresponding to thefirst interference pattern and the second interference pattern.

The apparatus for manufacturing a holographic optical element andapparatus for reconstructing a hologram according to the presentdisclosure is not limited to the configuration and the method of theembodiments described above, but the embodiments may be constructed byselectively combining all or a part of the embodiments to enable variousmodifications.

The particular implementations shown and described herein areillustrative examples of the inventive concept and are not intended tootherwise limit the scope of the inventive concept in any way. For thesake of brevity, conventional electronics, control systems, softwaredevelopment and other functional aspects of the systems may not bedescribed in detail. Furthermore, the connecting lines, or connectorsshown in the various figures presented are intended to representfunctional relationships and/or physical or logical couplings betweenthe various elements. It should be noted that many alternative oradditional functional relationships, physical connections or logicalconnections may be present in a practical device. Moreover, no item orcomponent is essential to the practice of the inventive concept unlessthe element is specifically described as “essential” or “critical.”

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the inventive concept (especially in the contextof the following claims) are to be construed to cover both the singularand the plural. Furthermore, recitation of ranges of values herein aremerely intended to serve as a shorthand method of referring individuallyto each separate value falling within the range, unless otherwiseindicated herein, and each separate value is incorporated into thespecification as if it were individually recited herein. Also, the stepsof all methods described herein can be performed in any suitable orderunless otherwise indicated herein or otherwise clearly contradicted bycontext. The present inventive concept is not limited to the describedorder of the steps. The use of any and all examples, or language (e.g.,“such as”) provided herein, is intended merely to better illuminate theinventive concept and does not pose a limitation on the scope of theinventive concept unless otherwise claimed. Numerous modifications andadaptations will be readily apparent to one of ordinary skill in the artwithout departing from the spirit and scope of the present inventiveconcept.

It should be understood that embodiments described herein should beconsidered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each embodimentshould typically be considered as available for other similar featuresor aspects in other embodiments.

While one or more embodiments have been described with reference to thefigures, it will be understood by those of ordinary skill in the artthat various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. An apparatus for manufacturing a holographicoptical element having different optical characteristics, the apparatuscomprising: a light emitting portion configured to sequentially emit afirst laser beam and a second laser beam; a beam splitter configured tosplit the first laser beam into a first signal beam and a firstreference beam, and split the second laser beam into a second signalbeam and a second reference beam; a hologram recording medium; a firstoptical system configured to emit the first signal beam to one surfaceof the hologram recording medium and the first reference beam to anothersurface of the hologram recording medium, and to record a firstinterference pattern of the first signal beam and the first referencebeam on the hologram recording medium; and a second optical systemcomprising a Fourier lens and configured to emit a second signal beammodulated by the Fourier lens to one surface of the hologram recordingmedium and a second reference beam to another surface of the hologramrecording medium, and to record a second interference pattern of themodulated second signal beam and the second reference beam on thehologram recording medium.
 2. The apparatus of claim 1, wherein energyof the modulated second signal beam and the second reference beamemitted to the hologram recording medium during recording of the secondinterference pattern is set to be greater than energy of the firstsignal beam and the first reference beam emitted to the hologramrecording medium during recording of the first interference pattern. 3.The apparatus of claim 1, wherein the light emitting portion emits thesecond laser beam longer than an emission time of the first laser beam.4. The apparatus of claim 1, wherein the hologram recording medium, onwhich the first interference pattern and the second interference patternare recorded, has optical characteristics of a mirror corresponding tothe first interference pattern and optical characteristics of a Fourierlens corresponding to the second interference pattern.